Web of deception

27 October 2010

It’s well known that some predators in the natural world use camouflage or stalking to catch their prey – but new research published in Proceedings of the Royal Society B shows that the assassin bug uses even more devious means to ensnare its victims.

Previous work has shown that many spiders detect insects and other prey that have become stuck in their web through the unique vibrations they make. This way, objects that fall on to the web such as fallen leaves and other debris can be ignored by the spider, because they don’t make the right pattern of vibrations. Likewise, a potential mate will make a specific set of vibrations on the web to show that he is interested, and the female predatory spider can respond accordingly.

The assassin bug Stenolemus bituberus likes to dine on carnivorous spiders, who might be expected to be tricky to catch. However, as its name might suggest, the assassin bug uses a clever strategy to lure spiders into its reach. Rather than quietly stalking the spider or camouflaging itself, the bug advertises its presence by mimicing the vibrations made by struggling prey as they lie tangled in the sticky spider silk. This immediately attracts the spider to the bug, which then pounces and devours the spider.

This might seem like a risky strategy – one might ask how the bug avoids getting eaten as the spider rushes to investigate what it thinks will be a tasty treat. However, the researchers discovered that the bug specifically mimics the vibrations characteristic of a small and feeble insect. This means that the spider almost always approaches more slowly than if it seems to be a large and possibly threatening insect caught in the web. While some spiders are thought to use this type of tactic to prey on other spiders, this is the first time that a non-spider has been shown to catch spiders in this fiendishly clever way.